Do Fruit Ripening Volatiles Enable Resource Specialism in Polyphagous Fruit Flies?

Abstract

Frugivorous tephritid fruit flies have lineages with high levels of host generalism. These insects use olfaction to locate fruits, but how they are able to recognize the odors of so many different host species is poorly understood. We used a series of behavioral experiments to investigate the role of fruit ripening volatiles as host cues in the Queensland fruit fly, Bactrocera tryoni (Froggatt), a polyphagous pest in Australia. Odors of mature guava (Psidium guajava) attracted female and male flies more strongly than three other ripening stages and guava pulp. We analyzed volatiles from guava odor and selected eleven compounds, all of which elicited an electrophysiological response in the antenna of female flies. Three of these, ethyl acetate, ethyl butyrate, and ethyl propionate, were released at the highest rates from the most attractive ripening stage. In behavioral trials, these three esters were not attractive individually, whereas a combination was necessary and sufficient in attracting female flies. The three-component blend was as attractive as the entire 11-component blend, which without these key volatiles was not attractive. Moreover, injecting low ranking hosts (squash and cucumber) with the three volatiles increased attraction in ovipositing female flies. These fruit flies are classed as generalists, but like many polyphagous insects they could be regarded as resource specialists, preferring specific plant reproductive stages with predictable odor cues. Exploring olfaction from this perspective could improve our understanding of host choice in polyphagous insects, and the selection of volatiles to be used as attractants in insect pest management.

Sampling technique biases in the analysis of fruit fly volatiles: a case study of Queensland fruit fly

“…Some of these compounds have been reported previously in fruits. For example, ethyl propanoate, which has a pineapple-like odor 51 , is a common volatile in many ripe fruits that attract B. tryoni females including mango and apple 52 . Ethyl propanoate has also been considered as an attractant for other frugivorous pest insects.…”

Translating olfactomes into attractants: shared volatiles provide attractive bridges for polyphagy in fruit flies

“…Jayanthi et al 2012Jayanthi et al , 2014a, fly species (e.g. B. tryoni, Cunningham et al 2016) and environmental cues (e.g. food and host plant odours, contextual odours), and pay particular attention to volatiles whose detection may have fallen below noise levels due to positional effects or low abundance of corresponding sensory neurons (Olsson & Hansson 2013;Biasazin et al 2014, Jacob et al 2017.…”

“…In contrast, our knowledge of tephritid olfaction is rather fragmentary (Fombong et al 2016), in spite of their global economic significance. In semi-field trials, Cunningham et al (2016) found a combination of only three short-chain aliphatic esters derived from guava that was attractive to the Queensland fruit fly, Bactrocera tryoni (Froggatt). While this does provide a horizon for using synthetic blends for monitoring or control of tephritids, the use of three highly related compounds leaves the vast majority of volatiles and their cognate olfactory channels 'untapped' (Siderhurst & Jang 2006Jayanthi et al 2012;Biasazin et al 2014).…”

Behavioral and Physiological Evidence for Palp Detection of the Male-Specific Attractant Cuelure in the Queensland Fruit Fly (Bactrocera tryoni)

“…In the last 50 years, substantial efforts have been invested into identifying visual and olfactory attractants to implement in “lure and kill” strategies as part of sustainable pest management programs. While B. tryoni females are attracted to a three-component mixture of fruit derived esters ( Cunningham et al, 2016 ), no effective lures have been developed so far. Male flies, on the other hand, are strongly attracted to the phytochemical compound raspberry ketone and its synthetic analog called “cuelure”.…”